Among sensors are a touch sensor which detects in contact with an object by sensing an impedance change depending on whether the object is contact with a touch pad or not, and a capacitive sensor which detects a position of an object by sensing a capacitance change varied by a user's adjustment, etc.
Sensitivity of the touch sensor and the capacitive sensor may vary depending on variation of an external environment such as power voltage, ambient temperature, ambient humidity, etc, regardless of whether the object is in contact with the touch pad or there is user adjustment. If the sensitivity becomes low, the touch sensor and the capacitive sensor may not sense the impedance change or the capacitive change.
FIG. 1 is a block diagram showing a configuration of a conventional pulse-pass type touch sensor, which includes a pulse signal generating part 10, a plurality of channels CH1 to CH(N) and a controller 12. Among the pulse channels CH1 to CH(N), the channel CH1 includes a pulse signal transmission part 2 and a pulse signal detection part 3.
The configuration of the touch sensor shown in FIG. 1 will be described as follows.
A clock signal generator 13 of the pulse signal generating part 10 generates a clock signal CLK to transmit the clock signal CLK to a signal delay circuit 14 and an AND gate 16.
The signal delay circuit 14 varies a phase delay time of the clock signal CLK in response to a pulse width control signal PCON transmitted from the controller 12.
An inverter 15 inverts a clock signal DCLK output from the signal delay circuit 14.
The AND gate 16 performs an AND operation on the clock signal CLK transmitted from the clock signal generator 13 and the clock signal DCLK transmitted via the signal delay circuit 14 and the inverter 15 to generate a pulse signal having a pulse width corresponding to the phase delay time of the signal delay circuit 14.
The pulse signal transmission part 2 of the channel CH1 is connected to a touch pad 5 in contact with a touch object having a predetermined capacitance (hereinafter, referred to as a “touch object”). The pulse signal transmission part 2 receives a pulse signal of the pulse signal generating part 10. When the touch object is not in contact with the touch pad 5, the pulse signal is directly transmitted to the pulse signal detection part 3. When the touch object is in contact with the touch pad 5, a pulse signal phase-delayed by the capacitance is transmitted to the pulse signal detection part 3.
The pulse signal detection part 3 of the channel CH1 checks the pulse signal transmitted by the pulse signal transmission part 2 with the clock signal CLK to output a non-phase-delayed pulse signal and not to output a phase-delayed pulse signal.
The controller 12 receives output of the respective pulse signals P1 to P(N) of the channels CH1 to CH(N) to check the pulse signals P1 to P(N) of the channels and obtain the channels CH1 to CH(N) having no output of the pulse signals P1 to P(N).
The controller 12 generates an output signal OUT informing a touch of the touch object to the channels CH1 to CH(N), depending on the detection result of the pulse signals P1 to P(N), to output the output signal OUT to an external device (not shown), and then generates a pulse width control signal PCON to correct a pulse width of the pulse signal to be appropriate for the current operating environment.
At this time, the controller 12 determines that the touch object is not in contact with the touch pad when the pulse signal detection part 3 detects a high level signal, and determines that the touch object is in contact with the touch pad when the pulse signal detection part 3 detects a low level signal for a certain time or more.
Touch sensitivity of the touch pad 5 in the touch sensor is varied depending on an operating environment of the touch sensor such as operating power voltage, ambient temperature, ambient humidity, and so on. Therefore, the pulse signal as an output signal of the pulse signal transmission part 2 detected by the pulse signal detection part 3 has a phase delay varied depending on the operating environment.
FIG. 2 is a flowchart showing the operation of the conventional touch sensor.
The operation of the conventional touch sensor of FIG. 2 will now be described with reference to FIG. 1.
The pulse signal generating part 10 generates a pulse signal having a predetermined pulse width in response to a pulse width control signal PCON of the controller 12 to output the pulse signal to the pulse signal transmission part 2 (S1).
When the touch object is in contact with the touch pad 5, the pulse signal transmission part 2 outputs a phase-delayed pulse signal (S2). And when the touch object is not in contact with the touch pad 5, the pulse signal transmission part 2 transmits a non-pulse-delayed pulse signal to the pulse signal detection part 3 (S3).
The pulse signal detection part 3 does not output the phase-delayed pulse signal, and outputs the non-phase-delayed pulse signal only (S4).
As a result of step S4, when the pulse signal is not transmitted, the controller 12 determines that the touch object is in contact with the touch pad 5 and informs the determination to a user or an external device (S5). Then, the controller 12 resets “non-contact time” and returns to step S1 to perform a new touch detection operation (S6).
As a result of the determination of step S4, when the pulse signal is transmitted, the controller 12 determines that the touch object is not in contact with the touch pad 5 and informs the determination to the external device (S7), and determines whether an impedance adjustment period has arrived (S8).
As a result of the determination of step S8, when the impedance adjustment period has not arrived, the controller 12 increases the current “non-contact time” to a set value, and returns to step S1 to perform a new touch detection operation (S9).
As a result of the determination of step S8, when the impedance adjustment period has arrived, the controller 12 performs the impedance adjustment operation to correct the pulse width of the pulse signal to be appropriate for the current operating environment of the touch sensor (S10).
After correcting the pulse width through the impedance adjustment operation (S10), the controller 12 resets the current non-contact time, and then returns to step S1 to newly perform the touch detection operation using the pulse signal, the impedance of which was adjusted.
FIG. 3 is a flowchart showing the impedance adjustment operation of FIG. 2.
The controller 12 determines whether the non-contact accumulation time arrives at a non-contact determination time in order to determine whether conditions for performing the impedance adjustment operation of the pulse signal are satisfied (S1-1).
As a result of the determination of step S1-1, when the non-contact accumulation time is smaller than the non-contact determination time, the controller 12 determines that the impedance adjustment operation has performed under an abnormal condition and terminates the impedance adjustment operation.
As a result of the determination of step S1-1, when the non-contact accumulation time is equal to or larger than the non-contact determination time, the controller 12 determines that the touch pad is in a non-contact state for a certain time and that it is the impedance adjustment operation time, and holds the current output state to prevent malfunction of the external device by an output signal of the touch sensor generated during the impedance adjustment operation (S1-3).
The controller 12 sets the pulse width of the pulse signal as a maximum value (S1-4), and determines whether the pulse signal is transmitted through the pulse signal detection part 3 (S1-5).
As a result of the determination of step S1-5, when the pulse signal is transmitted, the pulse width of the pulse signal is reduced to a set value (S1-6), and after returning to step S1-5, the pulse width of the pulse signal is sequentially reduced until the pulse signal is not transmitted.
As a result of the determination of step S1-5, when the pulse signal is not transmitted, the controller 12 obtains the current pulse width as a critical pulse width (S1-7), and determines whether a difference between the current critical pulse width and the critical pulse width during the previous impedance adjustment is larger than an allowable value (S1-8).
At this time, the allowable value is a value which can be set by a user for determining whether the impedance adjustment operation of the pulse signal is normal or not.
When the difference between the current critical pulse width and the critical pulse width during the previous impedance adjustment is larger than the allowable value, the controller 12 determines that the impedance adjustment operation has performed under an abnormal condition (S1-2), and terminates the impedance adjustment operation.
When the difference between the current critical pulse width and the critical pulse width during the previous impedance adjustment is smaller than or equal to the allowable value, the controller 12 determines that the impedance adjustment operation has performed under a normal condition, and then adds a margin pulse width to the current critical pulse width to obtain an impedance-adjusted pulse width appropriate for the current operating environment (S1-9).
At this time, the margin pulse width is a value which can be set by a user for representing a touch sensitivity of the touch pad 5.
The impedance-adjusted pulse width is a minimum pulse width that the pulse signal detection part 3 can determine whether the pulse signal is transmitted under the current operating environment.
Then, the controller 12 corrects the pulse signal to the impedance-adjusted pulse width (S1-10), and then terminates the impedance adjustment operation.
FIG. 4 is a block diagram showing a configuration of a conventional delay-chain type touch sensor. The delay-chain type touch sensor includes a pulse signal generating part 40, a reference delay signal generating part 41, a plurality of channels CH1 to CH(N), and a controller 44. The channel CH1 among the channels CH1 to CH(N) includes a pulse signal transmission part 41-1, a variable delay part 42-1, and a pulse signal detection part 43-1.
The pulse signal generating part 40 generates a predetermined size of pulse signal as an output pulse signal R_Sig to apply it to the reference delay signal generating part 41 and the pulse signal transmission parts 41-1 to 41-N.
The reference delay signal generating part 41 delays the signal R_Sig by a predetermined time regardless of contact of the touch object, and generates a reference delay signal Sig1.
The pulse signal transmission parts 41-1 to 41-N include touch pads PAD in contact with the touch object. When the touch object is in contact with the touch pad PAD, the pulse signal R_Sig is delayed more than the reference delay signal Sig1, and when the touch object is not in contact with the touch pad PAD, the pulse signal R_Sig is delayed less than the reference delay signal Sig1 to generate touch signals Sig2-1 to Sig2-N such that the reference delay signal Sig1 is different from the delay time.
The variable delay parts 42-1 to 42-N vary the delay time of the touch signals Sig2-1 to Sig2-N in response to control signals D1 to Dn supplied from the controller 44, and output variable delay signals VSig2-1 to VSig2-N depending on the varied delay time.
The pulse signal detection parts 43-1 to 43-N are synchronized to the reference delay signal Sig1 to sample and latch the variable delay signals VSig2-1 to VSig2-N, thereby outputting touch signals S1 to S(N).
When the touch object is in contact with the touch pad PAD to continuously output the touch signals S1 to S(N), the controller 44 detects that the touch sensor is in operation, and receives the touch signals S1 to S(N) from the pulse signal transmission parts 41-1 to 41-N corresponding to the contacted pads PAD to generate touch outputs TOut-1 to TOut-N. When the touch object is not in contact with the touch pad PAD and not to output touch signals S1 to S(N), the controller 44 detects that the touch pad PAD is in standby, and controls the control signal D1 to Dn supplied to the variable delay parts 42-1 to 42-N to adjust the impedance of the touch pad PAD, thereby adjusting the delay time.
In order to prevent general operations of the touch sensor being affected by adjustment of the control signals D1 to Dn during the impedance adjustment operation using adjustment of the control signals D1 to Dn to the variable delay parts 42-1 to 42-N, the controller 44 holds the latest touch outputs TOut-1 to TOut-N of the touch pads PAD, and sequentially adjusts the control signals D1 to Dn with respect to the variable delay parts 42-1 to 42-N.
Then, the controller 44 varies the control signals D1 to Dn to repeatedly adjust the delay time of the variable delay parts 42-1 to 42-N and extracts a delay time when the touch signals S1 to S(N) have the same value as when the touch object is in contact with the touch pad PAD, i.e., a control value of the control signal, thereby obtaining minimum delay values D1(TH) to Dn(TH).
Next, the controller 44 calculates differences between the minimum delay values D1(TH) to Dn(TH) and the impedance of the touch pad PAD to determine a control value, and transmits the determined control value as the control signals D1 to Dn to the variable delay part to substantially obtain an error margin of the touch sensor.
That is, in order to generate correct touch outputs S1 to S(N) when the touch object is in contact with the touch pad PAD, considering the touch sensitivity of the touch pad PAD when the touch object is not in contact with the touch pad PAD, the controller 44 controls the variable delay part to output the variable delay signals VSig2-1 to VSig2-N such that delay times of the reference delay signal Sig1 and the variable delay signals VSig2-1 to VSig2-N are different from each other.
The initial impedance of the touch pad is obtained through repeated experiments. The larger the size of the touch pad, the larger the initial impedance of the touch pad.
FIG. 5 is a flowchart showing the operation of the touch sensor of FIG. 4.
The pulse signal generating part 40 generates a predetermined magnitude of pulse signal as an output pulse signal R_Sig to apply it to the reference delay signal generating part 41 and the pulse signal transmission parts 41-1 to 41-N (S5-1).
When the touch object is in contact with the touch pad PAD, the pulse signal transmission parts 41-1 to 41-N delay the pulse signal R_Sig more than the reference delay signal Sig1 to generate transmission signals Sig2-1 to Sig2-N delayed more than the reference delay signal Sig1 (S5-2), and when the touch object is not in contact with the touch pad PAD, transmission signals Sig2-1 to Sig2-N delayed less than the reference delay signal Sig1 are generated.
That is, when the touch object is not in contact with the touch pad PAD, the delay time of the variable delay parts 42-1 to 42-N is added to the transmission signals Sig2-1 to Sig2-N delayed less than the reference delay signal Sig1 output from the pulse signal transmission parts 41-1 to 41-N, and thus variable delay signals VSig2-1 to VSig2-N delayed to be equal to the reference delay signal Sig1 are generated.
The variable delay parts 42-1 to 42-N receive the transmission signals Sig2-1 to Sig2-N of the pulse signal transmission parts 41-1 to 41-N, respectively. When the touch object is in contact with the touch pad PAD, the delay time is added to output the variable delay signals VSig2-1 to VSig2-N delayed more than the reference delay signal Sig1, and when the touch object is not in contact with the touch pad PAD, the variable delay signals VSig2-1 to VSig2-N delayed equal to or less than the reference delay signal Sig1 are output.
At this time, since the touch object is not in contact with the touch pad PAD, it will be appreciated that the variable delay signals VSig2-1 to VSig2-N output from the variable delay parts 42-1 to 42-N can be delayed less than the reference delay signal Sig1.
The pulse signal detection parts 43-1 to 43-N receive the reference delay signal Sig1 and the variable delay signals VSig2-1 to VSig2-N to sample and latch the variable delay signals VSig2-1 to VSig2-N synchronized with the reference delay signal Sig1 to thereby output the touch signals S1 to S(N).
The controller 44 determines whether the touch signals S1 to S(N) are varied (S5-4). When the touch object is in contact with the touch pad PAD to continuously vary the touch signals S1 to S(N), the touch sensor detects the operation state, and receives the touch signals S1 to S(N) from the pulse signal transmission parts 41-1 to 41-N corresponding to the contacted pad PAD to generate touch outputs TOut-1 to TOut-N (S5-5). When the touch object is not in contact with the touch pad PAD not to vary the touch signals S1 to S(N) for a predetermined time, the controller 44 detects that the touch sensor is in standby (S5-6), and controls the control signals D1 to Dn supplied to the variable delay parts 42-1 to 42-N to perform the impedance adjustment of the touch pad PAD, thereby adjusting the delay time (S5-7).
FIG. 6 is a flowchart showing the impedance adjustment of FIG. 5.
In order to perform the touch sensitivity adjustment of the touch pad, the controller 44 holds current touch outputs to prevent adjustment of the delay time of the variable delay part from affecting general operations (S6-1).
The controller 44 initializes a variable i (S6-2). The variable i represents a sequence of the variable delay parts included in the touch channels CH1 to CH(N) to perform the delay time adjustment.
The controller 44 increases the variable i by 1 (S6-3), and sets a delay value of an i-th variable delay part to be a minimum value (S6-4). Then, the controller 44 checks whether a touch signal value is equal to the same value (Si=1) as when the touch object is in contact with the touch pad (S6-5), increases the delay value of the i-th variable delay part by the set value when the check result is false (S6-6), and repeats step S6-5. When the check result is true, the controller 44 obtains the minimum delay value Di(TH) at this time (S6-7).
The controller 44 calculates a difference between the minimum delay value Di(TH) of the i-th variable delay part obtained during the previous delay time adjustment and the minimum delay value Di(TH) of the i-th variable delay part obtained during the current delay time adjustment, and compares the difference with the minimum value of the delay time generated when the touch object is in contact with the touch pad having a minimum size to check whether the current delay time adjustment is performed in a normal condition (S6-8).
When the difference between the minimum delay values is smaller than the minimum value generated when the touch object is in contact with the touch pad having a minimum size, the controller 44 determines that the touch object is not in contact with the touch pad, and in an opposite case, the controller 44 determines that the touch object is in contact with the touch pad.
As a result of the check of step S6-8, when the delay time adjustment is performed in a normal condition, the controller 44 calculates a difference between the value obtained through step S6-7 and the impedance of the touch pad obtained by an experiment to obtain a control value of the i-th variable delay part, and transmits the obtained control value as a control signal Di for adjusting the delay time of the i-th variable delay part (S6-9).
When the delay time adjustment is performed in an abnormal condition, the controller 44 goes to a touch output release step (S6-11) to cancel the delay time adjustment of the variable delay part and stand by the next adjustment.
Then, the controller 44 checks whether the i value is larger than or equal to the number of the variable delay parts installed in the touch sensor (S6-10).
When the i value is different from the number of the variable delay parts, the controller 44 returns to step S6-3 to perform the delay time adjustment of the next variable delay part, and when the i value is equal to the number of the variable delay parts, the controller 44 terminates the delay time adjustment to release the held touch output such that a novel value is updated when the touch object is in contact with the touch pad (S6-11).
In the touch sensor using the impedance adjustment method, when power is applied by a user being in contact with the touch pad, the touch sensor recognizes the user-touched state as an initial state to adjust the impedance, thereby unfortunately decreasing the impedance.
In addition, in a totally different environment, for example, in a state where the touch pad is submerged under water, the touch pad maintains a touched state. Therefore, even though the user attempts to touch the touch pad, the touch pad cannot be operated. That is, the sensitivity of the touch pad is decreased.